Black Swallowtail larva

I am certain. This may be somewhere around second or third instar. They start out quite small and are bird poop mimics. They change appearance as they grow. I have an almost complete series from egg to adult for the Black Swallowtail in my spottings starting here: http://www.projectnoah.org/spottings/159...

The link I provided on the ID suggestion also has a series photo if you scroll down a bit on the page that shows the general progression of size and appearance of these caterpillars through the different instars. :-)

Not sure you can see the scale of this, but it's pretty small - probably about 5/8".
Does that still compute for black swallowtail? I have seen them in this park, so it makes sense.

This looks like an earlier instar Black Swallowtail caterpillar. Anise Swallowtails do not occur in the eastern US, they are a western species.
Black swallowtail caterpillars can often be found on dill and fennel, as well as parsley.